The present invention relates to a chuck for releasably gripping a tool bit and, more particularly, to a keyless chuck and a method of assembly that provides a chuck which can be hand-tightened to grip a tool bit for reliable bi-directional operation, and, further, which can selectively self-tighten in response to torque applied through the chuck.
Various types of chucks are known for releasably gripping the shank portion of a tool bit. The common Jacobs-style chuck includes a nosepiece which contains gripping jaws and a rotatably mounted adjusting sleeve that is adjusted to cause the jaws to grip or release a tool bit. The adjusting sleeve includes axially extending gear teeth that are adapted to cooperate with a gear-type key to permit manual tightening and loosening of the jaws. The requirement for a separate key necessitates a minimum level of manual skill to effect proper tightening of the jaws to avoid any slippage between the tool bit and the jaws. Additionally, the tightening key represents another part which is subject to loss or wear.
A number of drill chucks, known generically as keyless chucks, have been designed in an effort to eliminate the need for the tightening key. These chucks are adapted to apply an initial, hand-tightening gripping force to the tool bit with the chuck self-tightening in response to torque applied through the tool bit and the chuck. Some of these keyless chucks have been provided with gripping jaws which toggle in response to the reaction torque encountered by the tool bit and still others have been provided with cam-like surfaces which contact and cooperate with the gripping jaws to increase the gripping force.
It is important for any keyless chuck to grip the tool bit in response to initial hand-tightening by the operator with sufficient gripping force so that the tool bit will not slip during either forward or reverse operation. It is also important that the chuck, as it self-tightens in response to applied torque, not over-tighten to the extent that the jaws effect local surface crushing of the tool bit stem or cause a lock-up situation in which the chuck cannot be loosened. Over-tightening and lock-up are generally not encountered with power tools intended for the consumer market. However, where keyless chucks are used on power tools intended for the commercial or industrial market, the substantial torques provided by these tools can induce undesired over-tightening or lock-up.
Known chuck designs have used one-way ratchet type mechanisms to allow a chuck to self-tighten in response to increased torque applied through the chuck and the tool bit. These designs allow the chuck to self-tighten in a progressive manner so that the tool bit will be reliably gripped as the applied torque is increased and prevent loosening of the chuck as a consequence of reverse operation. For example, U.S. Pat. No. 4,213,623 to Rohm discloses a drill chuck that includes an adjusting sleeve rotatably mounted to a chuck body for adjusting the gripping force applied by jaws mounted within the chuck body. The adjusting sleeve and the chuck body are coupled together by a one-way pawl and ratchet assembly. As the chuck is tightened in response to rotation of the adjusting sleeve relative to the chuck body, the pawl incrementally ratchets to a new position to maintain the tightened condition of the chuck and prevent unintentional counter-rotation of the adjusting sleeve and loosening of the gripping jaws. In another chuck, as disclosed in U.S. Pat. No. 3,506,277 to Harms, an adjusting sleeve is rotatably mounted upon a chuck body to allow tightening or loosening of the gripping jaws. The chuck body includes ratchet teeth formed on an axial end face. The teeth are engagable with a similar set of teeth on a user adjustable spring-biased sleeve. The teeth interengage to allow rotation of the adjusting sleeve to tighten the grip on the tool bit but prevent counter-rotation that would tend to loosen the tool bit. While these chucks are reasonably effective for their intended purpose, the chuck operator does not have full control over the manner by which the adjusting sleeve is operated and, accordingly, these chucks lack optimum operational flexibility.